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Construction’s sustainability challenge

The construction industry is on a mission to become greener by rediscovering traditional materials, inventing new ones and embracing digitisation.

Buildings tend to rise up around us, brick by brick. 

But in central Milan, one new installation literally grew out of the ground. The Circular Garden featured 60 arches made out of mycelium – or mushroom roots – arranged around the park’s paths for visitors to walk under. Each 4 metres tall, the arches took six weeks to grow and, at the end of their lifespan, returned back to earth in the form of compost in a perfect example of the circular economy in action. 

Designed by CRA-Carlo Ratti Associati in collaboration with oil and gas major ENI, the project forms a part of a growing movement to better attune the construction industry with the environment. 

“Fungus is actually a very interesting material, it is almost as strong as wood and it’s much lighter. It comes from soil and goes back to soil,” explains Carlo Ratti, founding partner of CRA and director of the MIT Senseable City Lab.

“We are seeing a big push towards circularity – the idea that everything you build, at the end of life you reuse or recycle it, you don’t send it to the landfill.” 

Such an approach is essential if countries are to meet their climate change targets. Buildings account for 36 per cent of global energy use through their construction and operation. They are also responsible for nearly 40 per cent of energy-related carbon dioxide emissions.1  

Sustainable construction is far from easy. With mycelium, durability is an issue – the fungus will eventually decay. The Circular Garden arches were designed only to be displayed for a month. 

That isn’t necessarily a big problem, though. While fast-decaying materials wouldn’t be suitable for buildings such as apartment blocks, they could be perfect for an exhibition pavilion or a pop-up restaurant. They could also work well when used as construction materials within buildings, where they are protected from the elements. 

Wood is another green material being explored by architects and construction firms – and increasingly championed by “smart city” organisations, which are keen to build sustainable metropolises. Politicians and regulators are increasingly getting onboard. Local government in Paris, for example, has mandated that any buildings lower than eight stories built for the 2024 Olympics must be made entirely from timber. France as a whole, meanwhile, is considering a law that would require all new public buildings to use at least 50 per cent wood and other sustainable materials. Other cities, such as Lucerne in Switzerland, are also planning initiatives to encourage wood construction.

“We are getting more and more requests for using wood,” Ratti says. “The interesting thing about wood is that it is totally circular, it is a carbon sink – a way to store carbon as long as you don’t burn it.”

Surprisingly, wood is also a fire-safe material, and can be used to offer fire resistance of up to two hours. It also chars and burns at a slow and even pace, making it predictable. In contrast, metal – such as steel – can melt in a rapid and unpredictable manner once it reaches critical temperature, potentially leading to sudden structural collapses.  

Although timber is relatively expensive, Europe’s plans for a new carbon tax could help shift the cost analysis in its favour. Ratti estimates that a tax of around USD50/tonne of CO2 would almost double the cost of concrete, but even a smaller levy would have a significant impact.

Technology is also being deployed so that timber can be used in the construction of larger buildings. In its  natural state, wood can’t easily be used for very tall skyscraper structures, not least because it tends to shrink when it dries. 

One possible solution is cross-laminated timber (CLT) – a wood panel material made by gluing together boards cut from a single log. Whereas building in wood was formerly confined to single family homes or small multi-family buildings, mid-rise and even high-rise buildings, can now entirely be erected from wood, using CLT technology. Japan’s Sumitomo Group is planning a 70-storey skyscraper made from CLT which could be completed by 2041. 

Stable and strong, CLT is used for the pre-fabrication of massive wooden, floors, and other structures that can be assembled much faster at the construction site, reducing costs, emissions, and as wood is lighter but has the same strength capabilities as other construction materials, but with a much lower impact on the environment.

“CLT is one of the best materials to start building a house like you are building a plane … What would take you 12 months in normal construction you can do in one month, so it’s huge, if you prefabricate all the elements,” says Ratti. “Today it is still more expensive than traditional construction but you save on time – so it becomes competitive if you want to be fast and to manage everything digitally. If you build quickly, you can sell your apartment faster and you need less working capital.”

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